Linear RF ion trap with high mass resolution

Abstract

In a linear ion trap in which an essentially quadrupole RF electrical field is generated between at least four rod-shaped electrodes, ions may be mass-selectively ejected orthogonally to the axis. An aspect of the invention comprises compensating for field irregularities along the axis of a linear ion trap, which result, at different ejection locations, in the ejection of ions of the same masses at slightly different times, by of measuring the ions that are ejected at the different ejection locations using a number of separate detectors, and correcting, after a mass calibration of each of the mass spectra, the time shifts of the various location-dependent mass spectra during their addition to a combined spectrum.

Description

PRIORITY INFORMATION[0001]This patent application claims priority from German patent application 10 2006 059 697.8 filed Dec. 18, 2006, which is hereby incorporated by reference.FIELD OF THE INVENTION[0002]The invention relates to a linear ion trap in which an essentially quadrupolar RF electrical field is generated between at least four rod-shaped electrodes, and which can mass-selectively eject ions orthogonally to the longitudinal axis of the ion trap.BACKGROUND OF THE INVENTION[0003]Linear ion traps are described in U.S. Pat. No. 5,420,425 to Bier et al. A particularly preferred embodiment, which is in fact applied in a successful commercial mass spectrometer, consists in assembling four hyperbolically shaped rods to create a very precise linear quadrupole system, making slots in two opposing rods, and mass-selectively ejecting the gas-cooled ions through the slots by radial resonant excitation. If the arrangement is perfectly symmetrical, the ions then emerge, during what is ca...

AI Technical Summary

Benefits of technology

The present invention relates to a method for measuring ions using a mass spectrometer. The method involves arranging a number of detectors along the axis of the mass spectrometer, and measuring the mass spectra of ions ejected from the detector at different locations. The mass spectra are then combined into a sum spectrum to correct for mass shifts caused by the ejection process. The method allows for accurate and efficient measurement of the mass spectra of ions, even at high speeds. The use of multiple detectors and nonlinear resonance phenomena can enhance the efficiency of the ejection process. The individual ion currents from the detectors are amplified and digitized, and the resulting sequences of values are added together to obtain the desired mass spectrum. The time shifts caused by the ejection process are calibrated to obtain accurate mass measurements. The technical effects of the invention include improved accuracy and efficiency in mass spectrometry and faster scan methods for a given mass resolution.

Problems solved by technology

A disadvantage of this arrangement is the extraordinarily high precision necessary to give a constant form and intensity to the RF electrical field at every cross-section along the axis.

The precision of the RF field is affected by disturbing effects at both ends of the pole rod system, disturbances at the ends of the slots, and, in particular, by the mechanical precision required for the shape and spacing of the pole rods.

This means that a mass spectrometer of this type does not offer usable resolution if it has such dimensional inaccuracies.

The usable mass range is also limited, as a resolution of a single mass unit is no longer available above 2000 Daltons.

The requirement for a mechanical precision of well below one micrometer is, however, almost impossible to meet.

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